The present invention relates to a process for increasing the speed of a rotatably mounted spinning or twisting ring from its rest state and for subsequently returning it to its rest state and to an apparatus for effecting this process. The apparatus forms part of a spinnning or twisting machine. The machine basically includes in addition to the ring, a traveler mounted on the ring, a driven spindle and a sleeve disposed thereon, Thread is wound on the sleeve as a result of its being drawn by the traveler, which, in turn, drives the ring.
Spinning or twisting rings of this type are disposed, as mentioned above, on spinning or twisting machines. Examples of such machines are ring spinning machines, ring twisting machines, draw-twisting machines, and the like. A machine of this type generally has a large number of these rings mounted on ring rails. The ring rails in turn are generally disposed on each longitudinal side of the machine. Each ring rail extends essentially over the entire length of the machine on its respective longitudinal side.
It has been the general practice in the art for the rings to be rigidly disposed on their respective ring rails. With this arrangement the traveler can obtain certain given speeds, which however, are too low for today's requirements. Thus for some time consideration has been given to mounting these rings in a rotatable manner, thereby enabling substantially higher traveler speeds and accordingly higher spindle speeds. As a result, the production capacity of the machine in question can be correspondingly increased.
It is undoubtedly possible in many cases to mount the rings in a rotatable manner by means of roller bearings but it is far better to use bearings which are virtually frictionless or at least frictionless at relatively low rotational speeds. It is known to provide aerostatic or aerodynamic air bearings for this purpose. Magnetic bearings which keep the ring in suspension can also be considered.
Even though the rings are rotatably mounted a problem still exists which has not yet been satisfactorily solved. This problem consists in bringing the spindles of a machine of this type from the inoperative or rest state to the operating speed (the operating speed is generally constant but it can be variable), and from the operating speed back to the rest state in order to stop spinning. This constitutes a problem because the rotatably mounted rings have a fairly considerable weight and associated relatively powerful moments of inertia which can produce extremely marked thread tension variations which cause thread breakage. Necking of the thread on the spindles especially during the terminating spinning phase, i.e., the speed at which the threads are guided to the spindles by the traveler, is greater than during the wind-on speed so that the thread balloons produced by the rotating traveler increase in size and collapse occurs. In addition, the threads twist in an uncontrolled manner about the sleeves disposed on the spindles or about the thread winding elements disposed on these sleeves. These produce thread breakage, incorrect winding onto the thread winding elements and other problems.
When yarns are spun on conventional ring spinning machines, even when air-cushioned spinning rings are used, limitations on the rotational speeds of the spindles are such as to prevent an improved spinning performance so that increased automation in the spinning process cannot be achieved.
In ring spinning there is produced between the cop on the spindle and the drawing system of the machine a thread tension which is used essentially to overcome frictional forces which are produced, especially the friction between the traveler and the ring. This system-dependent force is not uniform over the length of the thread extension. It can be measured in a known simple manner as the basic tension in the so-called spinning zone between the thread guide and the drawing system.
Under the influence of this basic tension, the centrifugal force in the thread balloon and the air friction, the thread forms between the traveler and the thread guide a spatially twisted curve which, in the projection at right angles to the axis, appears optically as the so-called "thread balloon."
The length of the thread in the balloon is greater than the distance between the traveler and the thread guide. The length increases the further the thread is deflected from the meridian plane defined by the traveler-spindle axis; in other words, the lower the thread tension under otherwise identical conditions the greater will be the length of the thread. Recognizing that the thread length can increase, it is nevertheless essential that the thread length does not fall below a minimum value as otherwise the thread curve (thread balloon) becomes unstable and results in necking and unavoidable thread breakage. In its stable phase this thread curve forms a flexible buffer zone which, if necessary, exerts a compensating action for short-term length or force variations. This occurs so long as the spatial twisting is sufficiently large so that the thread length or spatial curve generated adequately exceeds the shortest distance between the traveler and the thread guide; and so long as the actually free thread path can be achieved without having to generate excessively high force peaks for this purpose.
It is known that during spinning the above-described basic tension of the thread has constantly superimposed thereon low and high frequency periodic loading resulting from various causes. The associated load peaks increase in correspondence with the decrease in the excess thread which the balloon thread contains for flexible compensation, that is, in correspondence with the decrease in balloon height as the cop becomes increasingly full and the more the thread portion forming the balloon and disposed between the thread guide and the traveler approaches its shortest distance, or in other words becomes straight between the aforementioned spinning parts on account of increasing spinning tension and the more its deflection from the meridian plane becomes closer to zero.
It is perhaps less well know that the above-cited load peaks increase considerably as the rate of rotation of the spindle increases and that they are able to reach a multiple of the basic tension. As a result of the thread breakage which is directly associated therewith, increases in the rate of rotation and thus in the production rate are therefore restricted.
The above-described problem continues to exist in principle even when air-cushioned or magnetically mounted spinning rings are used because it is not possible to eliminate at the source of the problem the periodic load peaks caused by eccentricities of every kind in combination with the cyclical straining of the thread material as a result of periodic elongations. When air-cushioned spinning or twisting rings are used the traveler operates as a friction coupling with respect to the ring owing to centrifugal force and, for this reason, it is able, under certain conditions, to accelerate the air-cushioned spinning or twisting ring to such an extent that its rotational difference with respect to the traveler becomes zero and synchronous displacement begins. When the rotational speed and weight of the traveler are sufficiently high during synchronous displacement the sliding coupling consisting of the traveler and ring becomes a rigid, force-locking connection without any relative movement between the traveler and the ring.
As a result, the friction between the traveler and the ring is momentarily eliminated and thus, on account of the minimal air friction of the ring, the winding-on thread drawing the ring is simultaneously considerably slackened and, as a consequence, the thread tension in the balloon is suddenly reduced to the same extent. The result is a momentary broadening of the balloon diameter combined with a corresponding deflection of the balloon thread from its meridian plane which, at higher rotational speeds, generally leads to balloon collapse and thread breakage. The same result is obtained with air-cushioned spinning rings when the spinning apparatus is switched off, for example, when the cop is full and the rotational speed decreases rapidly while the ring and the traveler continue to rotate and retain their speed as a result of inertia and minimal friction. In the course thereof, the spun thread is no longer wound-on but is wound-off. As a result, the balloon expands and collapses or the thread is unhooked from the traveler. In both cases, the result is thread breakage.